Method and device for fast automatic adaptation of richness for internal combustion engine

ABSTRACT

The invention concerns a method for automatic adaptation of an injection engine by a computer connected to sensors. The sensors supply an engine filling parameter. An oxygen probe in the exhaust gases, defines, at each adapting cycle, a new line of control magnitude based on the filling parameter and using new coefficients computed from coordinates of two points. Corresponding corrected values of the control magnitude from a working line are filtered and stored during a preceding cycle. One of the two points is acquired previously, and then in adopting a new working line, an intermediate line between the new line and the previous working line is used. The invention is applicable to injection engine control.

TECHNICAL FIELD

The invention relates to a method and a device for fast automaticadaptation of air/fuel ratio for a fuel-injection engine, i.e. aninternal combustion engine of the controlled ignition type fitted with afuel-injection system, and having an oxygen sensor, commonly referred toas a λ sensor, which detects the oxygen content of the exhaust gases.

The invention therefore relates to fuel-injection engines, in particularfor motor vehicles, and a method of automatically adapting the controlcharacteristics governing the fuel supply, i.e. a system ofautomatically adapting parameters governing charging of the enginecylinders, and which offers an improvement on the automatic adaptationmethod known from FR-A-2 708 047. The method of rapid automaticadaptation proposed by the invention may simultaneously also be a methodof purging a circuit having a canister associated with the engine.

The invention also relates to an automatic adaptation device forimplementing the improved method proposed by the invention andincorporates a computer, which computer at least controls the injectionsystem but is preferably an engine control computer which additionallycontrols at least the ignition process.

BACKGROUND

It is common knowledge that, for a given type of engine, an adaptedengine control parameter or variable, such as the quantity of fuelinjected or the injection duration, given that the fuel flowrate-injection duration characteristic of the injectors is known, andwhich is referred to as a control variable throughout this description,is a known characteristic function which depends on parametersrepresentative of the charging of each of the engine cylinders, referredto as charging parameters throughout this description, and such as theabsolute pressure at the air intake manifold, the flow rate of the airadmitted to the engine or alternatively the angle at which a throttlevalve opens in a valve body on the air intake pipe to the engine, incombination with the speed or rotation speed of the engine. Inparticular, it is known that the basic fuel injection duration, fromwhich the injection duration effectively applied to the injectors isobtained, is defined as a function of the absolute pressure in the airintake pipe to the engine by means of a characteristic curve which canbe likened, in a steady state and across the greater part of theoperating range of the engine, to a straight-line curve with a slope G,known as gain, and an initial abscissa D, referred to as shift, for agiven engine speed. The increasing linear relationship between the basicinjection duration TinjB and the absolute intake pressure P cantherefore be written as follows:

TinjB=(P−D)×G,  (1)

where the intake pressure P represents the torque required from theengine, or load, at a given speed.

A known approach to controlling engine operation at an air/fuel ratio ofaround 1, corresponding to the stoichiometric mixture, is to determinean air/fuel ratio coefficient KO2 which is used to correct the basicinjection duration TinjB. This air/fuel ratio coefficient KO2 is derivedfrom a servoloop monitoring the air/fuel ratio R of the air-fuel mixturefrom an oxygen sensor positioned in the flow of the engine exhaust gas.In practice, the air/fuel ratio coefficient KO2 is between 0.75 and 1.25and constitutes a multiplicative correction factor for the basicinjection duration TinjB, which is therefore corrected by acting on KO2to an air/fuel ratio R equal to 1. Acting on KO2 generally consists inapplying value transitions to this coefficient on either side of a meanvalue, generally set at 1, for operating the engine in open loop.

Simultaneously, another known approach is to adapt the coefficients Dand G automatically as a means of keeping the air/fuel ratio coefficientKO2 as close to its mean value as possible.

Due in particular to manufacturing tolerances, wear and/or the need toreplace engine parts or components, the engines exhibit quite differentcharacteristics from one engine to another. However, in order to ensurethat engines continue to operate satisfactorily, there is a constantstriving towards simultaneously obtaining an air/fuel ratio signal R andan air/fuel ratio coefficient KO2 equal to 1 whilst automaticallycompensating for tolerances and drifts in engine characteristics byautomatically adapting the coefficients D and G of the straight-linecurve representing the operation of each engine.

A method of this type for automatically adapting the air/fuel ratio ofan injection engine is known from FR-A-2 708 047 and uses a computerwhich, on the one hand, is connected at least to sensors monitoringengine operating parameters, from which the computer receives at leastone engine speed signal and a signal enabling an engine chargingparameter P to be determined, this being the absolute pressure in an airintake pipe to the engine downstream of a throttle member such as abutterfly valve controlling the air supply rate, and to an oxygen sensorin the engine exhaust gas, from which the computer receives an air/fuelratio signal R, and, on the other hand, computes at least values of atleast one control variable, namely injection durations to be transmittedto at least one injector, which are obtained from basic values for thecontrol variable TinjB expressed as increasing linear functions of thecharging parameter P and represented by straight-line curves, eachdefined by two coefficients, these being a shift D of the initialcharging parameter and a gain G indicating the slope of the line suchthat TinjB=(P−D)×G, each basic value of the control variable TinjB beingcorrected to generate a corrected value for said control variableTinjCOR taking account of an air/fuel ratio coefficient KO2, to whichvalue transitions are applied as a function of the air/fuel ratio signalR in the operating zones of the engine in closed loop, and fixed at amean value in the operating zones of the engine in open loop in order toensure that engine operation is centred an air/fuel ratio R equal to 1,the shift D and the gain G also being automatically adapted in cycles toensure that the air/fuel ratio coefficient KO2 remains close to its meanvalue, by correction of any shift of this coefficient KO2 in takingaccount of the top and bottom values Ph and Pb of the charging parameterfor operating points of the engine in a stabilized state.

The teaching of the above-mentioned document is based in particular, fora stabilized engine and depending on certain previous operatingconditions of the engine, on enabling the air/fuel ratio to beautomatically adapted by modifying at least the shift D and preferablyonly the shift, within a first operating range of the engine, at lowintake pressure (for low charging parameter values) and by modifying atleast the gain G and preferably only the gain within a second operatingrange of the engine, at high intake pressure (for high chargingparameter values), these pressure ranges being set.

The disadvantage of this automatic adaptation system is that it isdifficult to operate in practice due to the fact that the frequency atwhich the high-pressure operating range occurs, in the order of 70 kPa,and hence the opportunity of being able to take real and multiplemeasurements of engine operating parameters during service, is lowwithin a standard cycle when driving a motor vehicle fitted with thisengine in the city.

Furthermore, according to the above-mentioned document, whenever anautomatic adaptation phase is initiated, it is allowed to continue for amaximum number of n1 cycles at most within the first operating range andfor a maximum number of n2 cycles at most within the second operatingrange and a new automatic adaptation of shift D or gain G is notpermitted until after all the automatic adaptation cycles permissible ingain and shift have been performed. The fact that the engine does notoperate often enough at the high-pressure range but all the automaticadaptation cycles at high pressure nevertheless have to be run beforereverting to automatic adaptation at low pressure means that the engineis not automatically adapted to gain and shift efficiently. This knownmethod therefore has the disadvantage of being too slow in terms of itsautomatic adaptation function.

The problem underlying the invention is to remedy the disadvantageoutlined above and to propose an improved method of automatic adaptationdesigned to determine dynamically the operating characteristic or lineof the engine in its linear section, allowing the gain G and shift D tobe computed simultaneously, these being the coefficients relating to theengine charging line.

Another objective of the invention is to propose an improved method ofautomatic adaptation which will advantageously enable controlled purgingof a canister purging circuit associated with the engine, in a manneralso known from FR-A-2 708 047, in which it is prohibited tosimultaneously have an automatic adaptation phase and a flow rate of ableed valve of the purging circuit.

SUMMARY OF THE INVENTION

To this end, the method proposed by the invention is characterized inthat it comprises steps which, for each new cycle of automaticadaptation of the order n, consist in defining a new characteristic linefor the control variable Tinj as a function of the charging parameter Pon the basis of new coefficients Dnew and Gnew, computed from thecharging parameter and control variable coordinates at two points, oneof which is at a top value Ph and the other at a bottom value Pb of thecharging parameter, and to which corrected values for the controlvariable TinjCORh and TinjCORb correspond, by applying the formulas:${Gnew} = {\frac{{TinjCORh} - {TinjCORb}}{{Ph} - {Pb}}\quad {and}}$${{Dnew} = {{Pb} - \frac{TinjCORb}{Gnew}}},\quad {and}$

validating a value Pk,n, measured when the engine is in a steady state,as a top value Ph,n or respectively as a bottom value Pb,n for thecharging parameter, correlating to it a basic value respectively for thetop or bottom control variable, in the order n, TinjBk,n taken from anoperating line filtered and stored in the computer during the precedingcycle n−1 and defined by the stored coefficients DFil,n−1 and GFil,n−1,and then correlating it to a corrected value for the control variableTinjCORk,n in order to obtain a first point, and taking as the secondpoint respectively the point having the top or bottom value for thecharging parameter from the two points stored in the computer during thepreceding cycle n−1, and having coordinates Pb,n−1, TinjCORb,n−1;Ph,n−1, TinjCORh,n−1, and then adopting as the new filtered operatingline, defined by new filtered coefficients DFil,n and GFil,n, anintermediate line between the stored line having coefficients DFil,n−1and GFil,n−1 and the new line defined by the newly computed coefficientsDnew and Gnew, and storing the new filtered coefficients GFil,n andDFil,n and substituting them for the preceding filtered coefficientsGFil,n−1 and DFil,n−1 to determine the next operating line for the nextautomatic adaptation cycle.

Accordingly, each new operating line of the engine is defined by its newfiltered coefficients GFil,n and DFil,n computed on the basis of thecoordinates (charging parameter and corrected control variable needed toobtain stoichiometric air/fuel ratio) of two operating points capturedduring stable operating phases of the engine, and one of which, havingcoordinates (Pb,n−1, TinjCORb,n−1) or, as is the case, (Ph,n−1,TinjCORh,n−1), is known and located on the preceding filtered operatingline, having coefficients DFil,n−1 and GFil,n−1, stored during thepreceding cycle n−1 following the last acquisition process, whilst theother point corresponds to a real value of the charging parameter Pk,nmeasured and validated at a stabilized speed, and a value of the controlvariable TinjBk,n taken from said preceding filtered operating line,then replaced by a corrected value TinjCORk,n to take account of thevalue of KO2 acquired simultaneously, the new filtered operating line,having filtered coefficients DFil,n and GFil.n, being part-way betweenthe filtered operating line of the preceding cycle and the new linecomputed directly from the coordinates of the two operating points thusdefined. The values for the new filtered coefficients GFil,n and DFil,nreplace the preceding coefficients GFil,n−1 and DFil,n−1 in memory andthe coordinates for the newly acquired point (Pk,n, TinjCORk,n) are alsostored and become the coordinates for one of the two points for the nextcycle of measurements.

Consequently, a recentering of the “first order” is obtained veryrapidly by modifying the adaptation terms, being the shift D and thegain G, because:

it is much easier to fulfil the adaptation conditions by suppressingspecific ranges of the charging parameter in order to adapt the shift Dand the gain G, and

the gain G and the shift D are computed simultaneously andinstantaneously so that the adaptation speed is no longer limited by theconvergence constraint which imposed very slow variations in theadaptation terms applied using the method known from the aforementioneddocument.

Advantageously, when the engine is running at a stabilized speed, themethod also consists in validating the measured value of the chargingparameter Pk,n as the new top Ph,n or bottom Pb,n value respectivelyonly if Pk,n is respectively above a suppressed adaptation band of apredetermined width and having the point with the bottom value storedduring the preceding cycle (Pb,n−1) as a lower limit, or below saidsuppressed adaptation band and having the point with the top valuestored during the preceding cycle (Ph,n−1) as an upper limit.Consequently, a minimum distance between the two points adopted, whichis necessary if the computation is to be accurate, defines the permittedadaptation zones. The condition used to validate the value of the newlyacquired charging parameter (Pk,n) is that this value is outside thesuppressed adaptation band AP, the width of which is predetermined.

Furthermore, with each new cycle of automatic adaptation of order n, themethod additionally consists in making a new suppressed adaptation bandcontiguous with the value entered for the charging parameter Pk,n andcomparing this latter value with the lower limit Pb,n−1 of the previoussuppressed adaptation band so that if Pk,n is lower than Pb,n−1, Pk,nwill then become the new lower limit Pb,n and the new upper limit willbecome: Ph,n=Pk,n+ΔP, ΔP being the width of the suppressed adaptationband, and if Pk,n is higher than Pb,n−1, Pk,n will then become the newupper limit Ph,n and the new lower limit becomes: Pb,n=Pk,n−ΔP.Accordingly, during a cycle, depending on whether Pk is found to beabove or below the suppressed adaptation band stored in memory, Pk willbecome the new top point Ph or the new bottom point Pb respectively,which determines the upper or lower limit respectively of the newadaptation band that will be suppressed ΔP.

Furthermore, in order to limit errors in the shift computation, it isnecessary to impose a maximum value on the bottom value of the chargingparameter, which means that the method will also consist in validatingthe measured value of this parameter Pk,n as a new bottom value Pb,nonly if, in addition, Pk,n is below or equal to a value threshold of thecharging parameter, for example in the order of 50 kPa, in calibration,if this charging parameter is the absolute pressure in the air intakepipe, downstream of the throttle member.

In accordance with this method, the engine speed is deemed to havestabilized if, after a predetermined number of transitions in theair/fuel ratio coefficient KO2 around its mean value and if the enginespeed N and the position of said throttle member are substantiallyconstant, the difference between the measured value of the chargingparameter Pk,n and a measured and filtered value of this parameterPkFil,n is below a value threshold, in whichPkFil,n=PkFil,n−1+k(Pk,n−PkFil,n−1), and where k is a factor between 0and 1. This being the case, a cycle of measurements and computations tofind the coefficients of the new filtered operating line DFil,n andGFil,n is initiated if the measured and filtered value PkFil,n of thecharging parameter falls outside the suppressed adaptation band locatedin the preceding cycle N−1 and Pk is replaced by PkFil in theaforementioned formulas in order to meet said conditions.

Consequently, in accordance with the invention, the coefficients of theengine operating line are stored in the computer and then constantlyupdated when the engine is operating, during repetitive measuring cyclesinitiated whenever the engine enters a phase of stabilized operatingspeed, at a charging parameter value which is outside the suppressedband. The new coefficients resulting from the current measurements takethe place of the preceding ones in the memory of the computer.

In accordance with one advantageous embodiment of the invention, aniterative correction of the coefficients defining the enginecharacteristic is applied more or less progressively in accordance witha logical filtering algorithm in order to avoid too abrupt variations inthe operating parameters as they are updated and so as to moveprogressively towards a mean characteristic. To this end, the methodalso consists in defining the new filtered operating line, havingcoefficients DFil,n and GFil,n, by applying a logical filtering processto the new computed coefficients Dnew and Gnew which consists in takinginto account only a fraction of the difference between Dnew and Gnewrespectively and the preceding filtered coefficients DFil,n−1 andDFil,n−1 respectively using an approximation of the first order, on thebasis of adaptation correction factors KD and KG, which range between 0and 1 and may be equal, such that:

DFil,n=DFil,n−1+KD(Dnew−DFil,n−1)

and

GFil,n=GFil,n−1+KG(Gnew−GFil,n−1).

The filtering rate applied may comprise several levels depending on theadaptation rate of the engine, on the basis of the values assumed by theair/fuel ratio coefficient KO2 and picked up in particular in each ofthe top and bottom adaptation ranges, i.e. outside the suppressedadaptation band.

To this end, the method also consists in applying adaptation correctionfactors KD and KG at several levels, depending on the control rate ofthe engine translated by the value of the air/fuel ratio coefficientKO2, the level of the factors KD and KG being selected depending on thevalue of KO2 as ascertained in each of the ranges of the top and bottomvalues of the charging parameter respectively above and below thecorresponding suppressed adaptation band.

In a preferred embodiment, a strong, mean or weak value is chosenrespectively for at least one of the factors KD and KG depending onwhether the air/fuel ratio coefficient KO2 is measured outside a band ofthe air/fuel ratio coefficient centred on the mean value of KO2 and ofpredetermined width, in the two charging parameter ranges above andbelow said suppressed adaptation band, or measured outside said air/fuelratio coefficient band in one of said charging parameter ranges above orbelow said suppressed adaptation band but inside said air/fuel ratiocoefficient band in the other of said upper and lower charging parameterranges and, finally, measured inside said air/fuel ratio coefficientband in the two upper and lower charging parameter ranges.

If the computer is switched off, which in practice is when the engine isswitched off, the computer memory specifically saves the lastcoefficients DFil and GFil stored, which will define the initialoperating line of the engine next time the computer is switched on,which in practice is when the engine is next started. A specificinitialisation system allows typical coefficients to be loaded wheneverthe computer is switched back on.

To this end, every time the engine is started, the method alsoadvantageously consists in determining, by means of the filteredoperating line, having coefficients DFil and Gfil, stored in memory onre-starting, two theoretical values for the control variable TinjCORhand TinjCORb corresponding to two values of the charging parameterselected from outside the usual range of values for said chargingparameter and which are a top initialisation value PhINIT and a bottominitialisation value PbINIT respectively, selecting a suppressedadaptation band essentially centred between PbINIT and PhINIT, with alower limit Pb higher than PbINIT and an upper limit Ph lower thanPhINIT, after which the measuring and computing cycle is then run as inthe continuous state, a new validated value being acquired for thecharging parameter if said new value falls outside the suppressedadaptation band and the coefficients DFil,n and GFil,n for the newfiltered operating line being computed on the basis of the new measuredand filtered value of the charging parameter PkFil and one of the twoinitialisation value points PhINIT or PbINIT of said parameter. Duringthe measuring and computing cycle following a re-start of the engine,the filtered value of the air/fuel ratio coefficient KO2 is alsoregarded as its mean value, i.e. 1 if KO2 is a multiplicative factor forcorrecting the basic values to generate corrected values of the controlvariable. Furthermore, when the engine is re-started, it is of advantageif the computer is adapted progressively to the real conditions bysetting the initial values for the adaptation correction factors KD andKG as a function of a fictitious degree of engine adaptation, forexample assuming that KO2 is inside said air/fuel ratio factor band foreach of the top and bottom bands of the charging parameter which arerespectively above and below the suppressed adaptation band.

Furthermore, before the computer is switched on for the first time, themethod also consists in pre-loading initial values GINIT and DINIT ofthe operating line coefficients into the computer memory, which aredefined experimentally for the specific type of engine and substitutingthem for the coefficients GFil and DFil stored for start-up purposes andnot yet existing.

If the engine co-operates with a purging circuit, fitted with a canisterto collect fuel vapours from at least one tank and connected to theengine intake pipe by an electrically controlled valve for purging thecanister, and whose rate is driven by the computer so that thesimultaneous timing of the purging valve and of the automatic adaptationsystem is prohibited, as disclosed in FR-A-2 708 047, it is of advantageto provide additional steps in the method proposed by the invention soas to supplement it, associating the automatic adaptation strategy witha strategy for purging the canister, priority being assigned to one orthe other of the two strategies depending on the engine adaptation leveland the degree to which the canister is filled. If the canister is veryfull of fuel vapours, the automatic adaptation will be inhibited. In thereverse situation and if the engine is not being sufficiently adapted ina top or bottom range of the charging parameter, i.e. if KO2 is notwithin said air/fuel ratio coefficient band in this top or bottom range,adaptation will take priority in this specific range of the chargingparameter. The priority between adaptation and purging the canister ismanaged by modulating the width of the suppressed adaptation band. Thissuppressed adaptation band is fully reserved for the canister purging,and the wider this suppressed band, the more the canister purging haspriority. In accordance with the method, it is therefore sufficient tomodulate this width relative to a nominal value of the suppressedadaptation band in order to manage the priority between adaptation andpurging the canister.

To this end, the method also consists in widening the suppressedadaptation band respectively towards the top values or towards thebottom values of the charging parameter if the engine regulation rate issatisfactory, depending on the value of the air/fuel ratio coefficientKO2, within the respective top or bottom range of the charging parameterwhich is above or below said suppressed adaptation band respectivelybefore it is widened.

However, in order to reactivate the adaptation options, the methodadvantageously also consists in making the widening of the suppressedadaptation band effective only during a predetermined period of time,assisted by a counter which is re-started with each automatic adaptationcycle to count down said period of time. Furthermore, so as to takeaccount of how full the canister is, the method may also consist indefining an estimated coefficient KCAN of the fuel contents in thepurging circuit, in the manner described in FR-A-2 708 049, to whichreference may be made for further information and advantages on thissubject. All that will be said here is that this coefficient KCAN may beworked out when purging is permitted on the basis of the deviation ofthe air/fuel ratio coefficient KO2 so that KCAN is increased ordecreased respectively if KO2 is respectively below or above its meanvalue. The method therefore consists in entering an automatic adaptationphase if KCAN falls below a predetermined threshold relating to the fuelcontent.

Another objective of the invention is a device for automaticallyadapting the air/fuel ratio of an injection engine, comprising acomputer connected to sensors detecting operating parameters of theengine as well as an oxygen sensor in the exhaust gas of the engine,said computer computing values of a control variable such as theinjection duration applied to at least one fuel injector of the engine,and obtained from base values TinjB expressed as increasing linearfunctions of a charging parameter of the engine, such as the pressure Pin an air intake pipe of the engine, with a shift D from the originalcharging parameter and a gain G corresponding to the slope of thecorresponding characteristic line, said base values TinjB of the controlvariable being corrected by means of an air/fuel ratio coefficient KO2determined by the computer as a function of the air/fuel ratio signal Rfrom the oxygen sensor operating in a closed loop and equal to a meanvalue when operating in an open loop, in order to centre the engineoperation on an air/fuel ratio equal to 1, the computer automaticallyadapting the shift D and the gain G in cycles to ensure that KO2 remainsclose to its mean value by correcting any deviation in KO2 and which ischaracterized in that the computer comprises at least one microprocessorprogrammed and/or set up so as to control running of the method proposedby the invention as described above.

Other advantages and features of the invention will become clear fromthe following description of an example of an embodiment, which is notrestrictive in any respect, and with reference to the drawings, ofwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an injection engine with a purgingcircuit with a canister, a control computer and a λ sensor,

FIG. 2 shows curves expressing the injection duration, giving an exampleof the engine control variable as a function of the absolute pressure inthe intake pipe and giving an example of the charging parameter of theengine, and

FIG. 3 is a schematic flow chart of the automatic adaptation system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 provides a schematic illustration of a four stroke-four cylinderand controlled ignition engine, shown generally by reference 1, fittedwith an injection system, of the multipoint type, for example. Thissystem comprises four injectors 2 each mounted in one of the fourrespective branches 3 downstream of an intake pipe 4, and each openinginto the cylinder head of the engine 1 on a level with the intakevalve(s) of a corresponding cylinder. A throttle valve 5 for controllingthe air intake rate is rotatably mounted in a throttle member 6 in theupstream part of the pipe 4, the throttle member 6 having a bypass duct7 on the throttle 5, the passage section of which is regulated by avalve shown by reference 8 and controlled by a stepper motor 9, forexample.

The injectors 2 are supplied with fuel at a pressure defined by aregulator 10, which is in turn supplied from a tank 11, closed by atight plug, by means of a pump 12 on a supply passage 13 on which afilter 14 is also mounted. The complement of the fuel quantity divertedby the regulator 10 to the injectors 2 is returned to the tank 11 via areturn passage 15.

The fuel vapours forming in the tank 11 in particular are collected by acanister 16, containing an absorbent charge for these vapours, activatedcarbon for example, and connected to the tank via a recovery line 17.The canister 16 has a vent 18 by means of which the tank is vented tothe open air and the canister 16 is connected to the intake pipe 4downstream of the throttle valve 5 via a suction line 19 on which anelectrically controlled valve 20 is mounted for purging the canister 16when a command is issued to the valve 20 to open. This valve 20 is asolenoid valve normally closed in the non-operating position and whenopen is controlled by a variable cyclical opening ratio (C.O.R).

The variable C.O.R. of this valve 20 and hence the rate at which thecanister 16 is purged of the fuel vapours it contains, as well as theposition of the electric stepper motor 9 are piloted by electriccommands transmitted to the valve 20 and the stepper motor 9 from acomputer 21 via conductors 22 and 23. Similarly, the opening duration orinjection duration of the injectors 2, on which the quantity of fuelinjected by each injector 2 into the corresponding cylinder depends(since the difference in fuel pressure applied to the injectors 2 isconstant and fixed by the regulator 10), is driven by electric commandsapplied by the computer 21 to the injectors 2 via a conductor 24.

These electric commands (injection duration, variable C.O.R., command tothe stepper motor) are worked out by the computer 21 on the basis ofsignals received from different sensors picking up engine operatingparameters, including a signal denoting the temperature of the intakeair 25 transmitted by a temperature sensor 26 positioned in the vein ofair, a signal indicating the absolute air intake pressure 27 transmittedby a pressure sensor 28 in the pipe 4, a temperature signal 29 for thecoolant water of the engine 1, supplied by a sensor which is notillustrated, and an engine speed signal 30, which enables the enginespeed N to be determined as well as the engine phases of the differentcylinders used to determine the injection timing as well as ignition ifthe computer 21 is an engine control computer.

The computer 21 also receives at 32 a signal 31 indicating the openingangle of the throttle 5 supplied by an appropriate sensor such as apotentiometer, which duplicates the angular position of the throttle 5,and is mounted on the rotation axis thereof.

The computer 21 also receives at 32 an air/fuel ratio signal R supplied,in the form of electric voltage, by an oxygen sensor 33 known as a ksensor, arranged in the exhaust gas 34 of the engine 1, which indicatesthe oxygen content thereof.

When the engine 1 is operating in closed loop, the air/fuel ratio signalR is used by the computer 21 to centre the engine operation on anair/fuel ratio equal to 1. To this end, the computer 21 firstly computesa control variable of the engine, for example a basic fuel injectionduration, with reference to a curve indicating, for a given type ofengine and for a given engine speed, the basic injection duration TinjBdependent on a charging parameter of the engine, for example theabsolute pressure P of intake air in the pipe 4, this characteristiccurve being tantamount to an increasing linear function, in a steadystate and across the greatest part of the effective operating range ofthe engine, defined by an initial shift D in pressure and by a gain Gcorresponding to the slope of the straight-line curve representing thisfunction. In very high and very low pressure zones, the curve exhibitsrounded S-shaped parts obtained from the straight line aftermultiplicative correction by a map factor K carto, which depends inparticular on the engine speed N and the pressure P in the pipe or theopening angle of the valve 5.

For a given speed N of the engine, this linear equation between thebasic injection duration TinjB and the intake pressure P, whichrepresents the load or torque required from the engine at a given enginespeed, is given by formula (1):

TinjB=(P−D)×G.  (1)

Applying this injection duration to the injectors, in particular aftercorrection as a function of engine speed, air temperature and a mapcorrection factor to define the injection duration actually applied tothe injectors, results in an air/fuel ratio signal R from the [ □] λsensor which is generally different from 1. The computer 21 increases orreduces TinjB to obtain an air/fuel ratio signal equal to 1. To thisend, the computer 21 works out an air/fuel ratio coefficient KO2 bywhich it multiplies the basic injection duration TinjB given by formula(1) in order to obtain a corrected injection duration TinjCOR inaccordance with formula (2): TinjCOR=TinjB×KO2.

In the zones when the engine is operating in open loop, the air/fuelratio coefficient KO2 is selected so as to be equal to 1. These zonesspecifically correspond to operation during which the λ sensor is faultyor at an air temperature below a threshold at which closed loop isactuated, for example when cold-starting the engine, or if the open loopis imposed by the engine speed or the opening angle of the valve, forexample during deceleration or at full load, or if the engine speed N ishigher than a given high threshold, for example 4500 rpm and, generallyspeaking, whenever the air/fuel ratio sought differs from 1.

After correction by multiplying by air/fuel ratio coefficient KO2, thevalue of the shift D or the gain G is modified by a cyclical automaticadaptation so that any variances in this air/fuel ratio coefficient KO2are corrected to ensure that it remains close to 1. In this example, KO2is deemed to be a multiplication correction factor of a mean value equalto 1.

This automatic adaptation is performed in the manner that will now bedescribed with reference to FIGS. 2 and 3.

In a steady state, the memory of the computer 21 contains the followingdata, stored during the preceding measuring and computing cycle, denotedas order n−1:

the filtered coefficients, as will be explained below, GFil,n−1 andDFil,n−1 of the preceding filtered operating line of the engine, shownby reference 35 in FIG. 2,

the pressure values, validated previously, for two operating points ofthe engine, one of which is at high pressure Ph,n−1 and the other at lowpressure Pb,n−1, and separated by a suppressed adaptation band of aconstant predetermined width AP of 20 kPa, for example, and thecorresponding corrected injection durations TinjCORh,n−1 andTinjCORb,n−1, so that the computer has all the corrected pressure andinjection duration coordinates for two points A and B on the precedingfiltered operating line 35 (GFil,N−1 and DFil,n−1), as illustrated inFIG. 2,

information about the adaptation level of the engine in each of therespective pressure ranges above and below the suppressed band ΔP, thisinformation being given by a flag of value 1 or 0 depending on whetherthe adaptation level of the engine is good or poor, as a function of themeasured value of the air/fuel ratio coefficient KO2 relative to avariance threshold on its mean value 1, as will be explained below,

parameters for an initialisation state, described below, and appliedwhenever the engine is started.

The computer also has in memory a certain number of parameters andcoefficients which might assume one or more constant values asstipulated below.

A new measuring and computing cycle for automatic adaptation of order ncommences with a search for and acquisition of an operating point of theengine in a stabilized state, outside the suppressed adaptation band ΔP.

On the basis of each power modification required (translated by avariation in at least the pressure Pk of the air admitted to the engineor the position of the valve 5 for the intake air), above a specificdefined threshold, the computer continuously compares the pressure Pk inthe intake pipe 4 with a filtered value PkFil of this pressure in orderto eliminate slight pressure fluctuations by a first order filteringprocess, known per se, and with a phase shift delayed by one cycle, inaccordance with the formula:

PkFil,n=PkFil,n−1+k(Pk,n−PkFil,n−1),

where k is a factor between 0 and 1 and PkFil,n−1 was stored in thecomputer during the preceding cycle n−1.

When the valve 5 opening and the engine speed N are substantiallyconstant, as soon as the difference between the measured pressure Pk,nand the measured and filtered pressure PkFil,n falls below a giventhreshold S1, of a low value, once a given number of transitions of KO2around its mean value 1 has been detected, the engine is considered asstabilized.

If, in addition, the measured pressure Pk,n or the filtered pressurePkFil,n, which is not very different from it, is outside the suppressedadaptation band, corresponding to the pressure band of width ΔPpositioned during the preceding cycle n−1 and stored in the computer,the new cycle of order n for measuring and computing coefficients forthe new filtered operating line (DFil,n and GFil,n) is initiated. Thevalues of the intake pressure Pk,n, its filtered value PkFil,n and acorresponding mean or filtered value KO2Fil,n of KO2 are entered andstored in the computer with:

KO2Fil,n−KO2Fil,n−1+α(KO2,n−KO2Fil,n−1), α being a factor between 0 and1.

Since the filtered pressure PkFil,n is assumed to be outside thesuppressed adaptation band ΔP of the preceding cycle, a new suppressedband of a same width ΔP is positioned so as to be contiguous with theentered pressure Pk,n, which is compared with the lower pressure limitPb,n−1 of the preceding suppressed adaptation band (Pb,n−1; Ph,n−1).

If Pk,n<Pb,n−1, Pk,n becomes the new lower limit of the new suppressedband: Pb,n=Pk,n and the upper limit then becomes Ph,n=Pb,n+ΔP.

If Pk,n>Pb,n−1, Pk,n becomes the new upper limit of the new suppressedband: Ph,n=Pk,n and the lower limit of said new suppressed band thenbecomes Pb,n=Ph,n−ΔP.

However, in order to obtain better accuracy in measuring the shift D, afurther condition is added to that defined above. This further conditionconsists in not validating the measured pressure Pk,n as a new bottompressure Pb,n unless, in addition, Pk,n is less than or equal to apressure threshold Psb, in the order of 50 kPa for example.

Generally speaking, in a stabilized engine state, the measured pressurePk,n is not validated as a new top pressure Ph,n unless Pk,n is greaterthan a pressure band ΔP of predetermined width, corresponding to asuppressed adaptation, and having Pb,n−1 as its lower limit, whereasPk,n is not validated as a new bottom pressure Pb,n unless Pk,n is belowthe pressure band ΔP and has Ph,n−1 as its upper limit and if, inaddition, Pk,n is less than or equal to said pressure threshold Psb.

If Pk,n is outside the band ΔP and for example is equal to Ph,n becauseit is above this band Δp as illustrated in FIG. 2, Pk,n corresponds, onthe preceding operating line that was stored and filtered(GFil,n−1−DFil,n−1), to a base injection duration TinjBk,n which thecomputer 21 multiplies by the measured KO2,n or measured and filteredKO2Fil,n air/fuel ratio coefficient in order to obtain a correctedinjection duration TinjCORk,n.

Accordingly, a new point C is obtained having coordinates (Pk,n;TinjCORk,n) which replaces one of the two points A and B of knowncoordinates and stored for computing the stored operating line 35 havingcoefficients GFil,n−1 and DFil,n−1, the other of the two points A or Bbeing used with the new point C to compute a new operating line 36having coefficients Gnew, Dnew. If Pk,n=Ph,n (as is the case in FIG. 2),then the third point C replaces point A having coordinates (Ph,n−1;TinjCORh,n−1) so that the new operating line 36 having coefficients Gnewand Dnew can be computed from points B and C, whereas if Pk,n=Pb,n, thenpoint C will replace point B having coordinates (Pb,n−1; TinjCORb,n−1)and the new operating line having coefficients Gnew, Dnew is obtainedfrom points C and A.

In other words, once the filtered pressure PkFil,n of the measuredpressure Pk,n is outside the pressure band ΔP positioned during thepreceding cycle n−1, the coefficients in memory for the previousoperating line 35 GFil,n−1 and DFil,n−1 allow the basic injectionduration TinjBk,n corresponding to the value PkFil,n to be computed, anddepending on whether Pk,n=Ph,n or =Pb,n, the following is calculated:

TinjBh,n=(Ph,n−DFil,n−1)×GFil,n−1

and

TinjBb,n=(Pb,n−DFil,n−1)×GFil,n−1.

These basic injection durations must be corrected in order to takeaccount of the adaptation quality of the engine, translated by themeasured and filtered value of KO2 at the acquisition step so that:

TinjCORh,n=TinjBh,n×KO2Fil,n

and

TinjCORb,n=TinjBb,n×KO2Fil,n.

The new operating line 36 is defined using the coordinates of the newlyacquired point (Ph,n; TinjCORh,n) or (Pb,n; TinjCORb,n) and those of thelast additional point previously acquired in the preceding cycle n−1. Inorder to simplify the description of this example showing how theinvention is implemented, it will be assumed below that the point newlyacquired is a high pressure point.

The coefficients of the new operating line 36 are computed using theequations:${{Gnew} = {\frac{{TinjCORh} - {TinjCORb}}{{Ph} - {Pb}}\quad {and}}}\quad$$\quad {{Dnew} = {{Pb} - \frac{TinjCORb}{Gnew}}}$

In order to avoid too rapid variations in the coefficients of the engineoperating line during an automatic adaptation, the new operating line 37of order n now stored is a new operating line which is filtered, beingdefined by new filtered coefficients DFil,n and GFil,n and which is anintermediate line 37 between the stored line 35 of order n−1 and havingcoefficients DFil,n−1 and GFil,n−1 and the new line 36 defined by thenew computed coefficients Dnew and Gnew. To this end, it is ofparticular advantage to find the coefficients of the new filteredoperating line 37 by applying a logical filter to the new computedcoefficients Dnew and Gnew, which consists in taking account of only afraction of the variance found between each of the new computedcoefficients Gnew and Dnew and the preceding filtered coefficientsGFil,n−1 and DFil,n. The new coefficients GFil,n and DFil,n are thusobtained, which are applied and stored, using adaptation correctionfactors KD and KG, ranging between 0 and 1, which may be different fromone another or the same, and such that the new filtered coefficients areobtained by the following equations:

DFil,n=DFil,n−1+KD(Dnew−DFil,n−1)

and

GFil,n=GFil,n−1+KG(Gnew−GFil,n−1).

The new filtered coefficients GFil,n and DFil,n are then stored andsubstituted for the preceding filtered coefficients GFil,n−1 andDFil,n−1 in order to determine the next operating line during the nextautomatic adaptation cycle of order n+1. Consequently, the engine willthen operate on the line (GFil,n; DFil,n) until a new measuring cycleoccurs, starting with a new measurement of Pk and its possiblevalidation, which defines a new line. The different lines so definedform a dynamic cloud around a mean line.

As far as the adaptation correction factors KD and KG are concerned, thefactors are applied at several levels, depending on the regulation rateof the engine, translated by the value of the air/fuel ratio coefficientKO2. The level of the factors KD and KG is selected as a function of thevalue of KO2 found in each of the high and low pressure ranges, whichare respectively above and below the corresponding suppressed adaptationband ΔP, in the manner described below.

In particular, the method may consist in selecting, for each of the twofactors KD and KG, three different values, which will be a high value,for example 0.5, a mean value, for example 0.1, and a low value, forexample 0.05, depending on the value of the air/fuel ratio coefficientKO2 measured in the high and low pressure ranges on either side of thissuppressed pressure range.

These three separate values for the adaptation correction factors KD andKG or the factor K if KD=KG=K, are useful because they allow theadaptation speed to be optimized as a function of the level of theengine adaptation found in the two adaptation ranges (high pressurerange and low pressure range) and represented by a flag Fb or Fhassociated respectively with the low pressure range or the high pressurerange. The high, mean and low values of the factors KG and KD thereforecorrespond to a rapid, mean or slow adaptation respectively and arechosen depending on whether the measured and filtered air/fuel ratiocoefficient KO2Fil exhibits a variance greater or less than a giventhreshold variance of 3.5% for example, with respect to its mean value1, in one and/or the other of the two high and low pressure ranges. Whenacquiring a low pressure point Pb or a high pressure point Phrespectively, the flag Fb or Fh associated respectively with the lowpressure range or the high pressure range is assigned a value whichdepends on the degree of adaptation of the engine and is set at 0 if theengine is not very well adapted and 1 if the engine is in the adaptationrange defined by said variance threshold on the mean value of KO2 sothat:

if Pk=Pb and KO2Fil is between 0.965 and 1.035 (i.e. 1±0.035), thenFb=1,

if Pk=Pb and KO2Fil<0.965 or KO2Fil>1.035, then

Fb=0,

if Pk=Ph and KO2Fil is between 0.965 and 1.035, then

Fh=1 and

if Pk=Ph and KO2Fil<0.965 or KO2Fil>1.035,

then Fh=0.

The table (given at the end of the description) gives two examples ofhigh, mean and low values for the factors KD and KG as a function of thevalues of the flags Fb and Fh, which in turn depend on the values of KO2in the high and low pressure ranges, the values for KD and KG optionallybeing different as in example I and of equal value for K=KD=KG as inexample II.

The value of Fb or respectively of Fh is updated and stored along withthe corresponding value of KO2Fil with every pressure measurement PkFilthat is validated.

Whenever the engine is started up, the memory of the computer 21contains a filtered operating line having coefficients DFil and GFilstored at the end of the last adaptation cycle run before the engine wasswitched off. This line having coefficients DFil and GFil is used todetermine theoretical corrected injection durations TinjCORh andTinjCORb corresponding to two selected intake pressures selected fromoutside the usual pressure range and which are respectively aninitialisation high pressure PhINIT, in the order of 90 kPa for example,and an initialisation low pressure PbINIT, in the order of 30 kPa forexample. A suppressed adaptation band ΔpINIT is also selected,essentially centred between PbINIT and PhINIT, and having a lower limitcorresponding for example to the low pressure threshold Psb, for example50 kPa, and a width ΔpINIT of 20 kPa for example, which gives an upperlimit or threshold high pressure of 70 kPa for this example. Onre-starting, it also be assumed that KO2Fil=1.

The measuring and computing cycle then runs as for the steady state, anew pressure point Pk being acquired and validated if it is outside thesuppressed band ΔpINIT, and the coefficients DFil,n and GFil,n computedfor the new filtered operating line using the new measured and filteredpressure PkFil,n and one of the two initialisation pressure pointsPhINIT or PbINIT. Furthermore, when the engine is re-started, thecomputer 21 is progressively adapted to the real conditions by settingthe initial values for the adaptation correction factors KD and KGdepending on a fictitious degree of adaptation of the engine. Let usassume, for example, that the engine is well adapted on start-up, inwhich case the flags Fb and Fh are equal to 1 and KG and KD are 0.05 asin the previous example.

When the computer 21 is manufactured or before it is initially broughtinto operation, the memory of the computer 21 is pre-loaded with initialvalues GINIT and DINIT for the coefficients of the operating line, whichwill have been defined experimentally specifically for the type ofengine. The first time the computer 21 is switched on, GFil and DFil areinitialized at the calibration values GINIT and DINIT. These calibrationvalues are thus substituted for the coefficients GFil and DFil the firsttime the engine is started up. The method then runs as described aboveafter being restarted.

In order to improve the co-existence of the automatic adaptationstrategy described above with the strategy for purging the canister 16,this purging taking place in particular when the computer 21 issues acommand to open the valve 20 when the intake pressure points are withinthe suppressed adaptation band during engine operation, priority isassigned to the different strategies depending on the adaptation levelof the engine and the degree to which the canister 16 is filled withfuel vapor. A system of assessing a coefficient KCAN indicating the fuelcontent of the canister 16 and its purging circuit is known from EP-A-0636 778 and FR-A-2 708 049 in particular, whereby this coefficient KCANis computed when a purging operation is permitted (valve 20 has beenopened by the computer 21) based on the drift in the air/fuel ratiocoefficient KO2 so that KCAN is increased if KO2 is below its mean valueand KCAN is decreased if KO2 is above its mean value. If the canister isvery full, KCAN is higher than a predetermined threshold for fuelcontent and, in accordance with the method proposed by the invention,adaptation will then be suppressed. If, on the other hand, KCAN fallsbelow said fuel content threshold, the computer 21 will permitinitiation of the automatic adaptation phase, which suppresses the flowthrough the purging valve 20 simultaneously with the automaticadaptation.

If the engine is not being sufficiently adapted within the high or lowpressure range, i.e. if Fh or Fb is equal to 0, adaptation will takepriority in the pressure range in question. If, on the other hand,adaptation is sufficient (Fh or Fb=1), priority for the time being canbe given to purging within the pressure range where adaptation is goodin addition to the exclusivity assigned to purging in the suppressedadaptation band. Priority is managed by modulating the width of thesuppressed adaptation band. In effect, within this band, adaptation issuppressed and, as mentioned above, it is natural to dedicate this bandentirely to purging. The wider this band is, the higher the priorityassigned to purging. The method of the invention therefore proposesmodulating the width of this suppressed adaptation band relative to anominal value in order to manage priority between purging andadaptation. To this end, the suppressed adaptation band, which is of anominal width ΔPINIT, is widened by a margin referred to as a top margintowards the high pressures and/or is widened by another margin, referredto as the bottom margin, towards the low pressures if the regulationrate of the engine is satisfactory in the high pressure range (Fh=1)and/or in the low pressure range (Fb=1), as a function of the value ofthe air/fuel ratio coefficient KO2 in the high pressure range and/or inthe low pressure range, which are respectively above and below thesuppressed adaptation band of a nominal width ΔPINIT, before beingwidened by one and/or the other margin.

By way of example, if ΔPINIT=20 kPa and each of the top and bottommargins is set at a calibration value of 10 kPa if Fh or Fb=1, or isequal to 0 if Fh or Fb=0, then the suppressed automatic adaptation bandmay assume three separate values which are 20 kPa if the two margins arezero, 30 kPa if a single margin is added to ΔPINIT or 40 kPa if ΔPINITis widened by the two margins. This band, which may be more or lesswide, is entirely dedicated to purging and the purging operationtherefore assumes a higher or lower priority depending on the width ofthis band. During the initialisation phase once the engine has beenswitched on, the margins are zero and the suppressed adaptation band islimited to the value of ΔPNIT so that adaptation takes priority.However, the limitation of Pb to the maximum value for the bottompressure Psb continues to be applied.

Widening the suppressed adaptation band on the side or the sides atwhich the engine is well adapted in fact procures a gain in time so thatthe purging operation can be run. However, so as not to penalize theadaptation process, this widening of the suppressed adaptation band willonly be effective during a predetermined period of time, for examplethree minutes, which is counted back by means of a counter actuated witheach automatic adaptation cycle so that the adaptation options can bebrought back into play at the end of this predetermined period of time.

The flow chart of the adaptation described above and implemented by thecomputer 21, which comprises at least one programmed microprocessorand/or is configured to control the process outlined above, isschematically illustrated in FIG. 3.

In FIG. 3, the step at which voltage 38 is applied implies that, if thisis the first time the computer 21 has been switched on, theinitialisation values GINIT and DINIT will be taken into account for thecoefficients GFil and DFil of the operating line stored during the firstinitialisation at 39. The next step 40 is the step at which theadaptation ranges on either side of the suppressed adaptation band aredefined on the basis of the nominal and initial value ΔPINIT, themaximum bottom pressure threshold Psb and flags indicating theadaptation of the engine Fb and Fh, selected to as to be equal to 1 atstep 41. The next step 42 consists in computing the theoretical andinitial values of TinjCORb and TinjCORh from the values of GFil, DFil,PbINIT and PhINIT and for KO2Fil=1, which are recorded at 43. The nextstep 44 consists in verifying the conditions for initiating adaptation.Adaptation is initiated if the current pressure in the pipe Pk is withinone of the permitted adaptation ranges and if the engine stability isverified, i.e. if the engine is operating in a stabilized mode in whichPk−PkFil<S1 (pressure threshold) and if the air temperature on the onehand and the engine coolant liquid (generally water) temperature on theother are above respective thresholds, as indicated at 45. As adaptationis initiated, the angle of the throttle valve 5 will be stored at 46. Inparallel, a command to suppress purging is transmitted at 47, optionallyin conjunction with commands to suppress operation of a valve forrecycling the exhaust gases and/or any other accessory whose operationdrives a modification of the air/fuel ratio. At the next step 48,adaptation is abandoned if at least one of the conditions promptinginitiation of the adaptation at 44 is no longer verified or if thevariation in the angle of the throttle valve 5 relative to the anglestored at 46 is higher than a threshold or alternatively if the numberof transitions of the signal KO2 from the onset of adaptation at 44 ishigher than a threshold SKO2max. At the next step 49, the adaptation isvalidated if the number of transitions of the signal KO2 since the onsetof adaptation at 44 is higher than a minimum threshold SKO2min, asindicated at 50. The minimum and maximum threshold conditions SKO2minand SKO2max for the transitions of KO2 limit the time spent onadaptation whilst guaranteeing an effective stability of theacquisitions needed for the computations, the stabilization of KO2,Filbeing indicative of the drift of the air/fuel ratio and stabilization ofthe filtered pressure PkFil being representative of the engine load. Ifthe adaptation is not validated, the system will return to step 44 atwhich adaptation is initiated whereas if the adaptation is validated,the process moves on to 51, where the signals KO2Fil and PkFil arestored, after which the coefficients Gnew and Dnew are computed at 52 inthe manner described above, followed by the selection of adaptationcorrection factors KG and KD at 53, also as described above and, at 54,computation of the coefficients for the new stored operating lineGFil,n; DFil,n and finally, at 55, computation of the pressure limitsPb,n and Ph,n defining the suppressed adaptation band stored for thenext cycle.

KO2Fil Ex. 2 High pressure Low pressure Ex. 1 KD = K Fb range range FnKD KG KG = K 1 0.965 < KO2 < 0.965 < KO2 < 1,035 1 0.05 0.05 0.05 1.0351 0.965 < KO2 < KO2 < 0.965 0 0.05 0.10 0.10 1.035 or 1.035 < KO2 0 KO2< 0.965 0.965 < KO2 < 1.035 1 0.10 0.05 0.10 Or 1.035 < KO2 0 KO2 <0.965 KO2 < 0.965 0 0.50 0.50 0.50 Or Or 1.035 < KO2 1.035 < KO2

What is claimed is:
 1. A method of automatically adapting the air/fuelratio of an injection engine (1) by means of a computer (21) which, onthe one hand, is connected at least to sensors (26, 28) monitoringoperating parameters of the engine (1), from which the computer receivesat least one engine speed signal (30) and a signal (27) enabling anengine charging parameter (P) to be determined, and to an oxygen sensor(33) in the exhaust gas of the engine (1), from which the computerreceives an air/fuel ratio signal (R), and, on the other hand, computesat least values for at least one control variable to be transmitted toat least one injector (2) which are obtained from basic values for thecontrol variable (TinjB) expressed as increasing linear functions of thecharging parameter (P) and represented by straight-line curves, eachdefined by two coefficients, these being a shift (D) from the initialcharging parameter and a gain (G) indicating the slope of the line suchthat TinjB=(P−D)×G, each basic value of the control variable (TinjB)being corrected to generate a corrected value for said control variable(TinjCOR) taking account of an air/fuel ratio coefficient (KO2), towhich value transitions are applied as a function of the air/fuel ratiosignal (R) in the operating zones of the engine (1) in closed loop, andfixed at a mean value in the operating zones of the engine (1) in openloop in order to ensure that operation of the engine (1) is centered onan air/fuel ratio (R) equal to 1, the shift (D) and the gain (G) alsobeing automatically adapted in cycles to ensure that the air/fuel ratiocoefficient (KO2) remains close to its mean value by correction of anyshift in this coefficient (KO2) by taking account of top and bottomvalues (Ph and Pb) of the charging parameter for operating points of theengine (1) in a stabilized state, characterized in that it comprisessteps which, for each new cycle of automatic adaptation of the order n,consist in defining a new characteristic line for the control variable(Tinj) as a function of the charging parameter (P) on the basis of newcoefficients (Dnew) and (Gnew), computed from the charging parameter andcontrol variable coordinates at two points, one of which is at a topvalue (Ph) and the other at a bottom value (Pb) of the chargingparameter, and to which corrected values for the control variable(TinjCORh and TinjCORb) correspond, by applying the formulas:${Gnew} = {\frac{{TinjCORh} - {TinjCORb}}{{Ph} - {Pb}}\quad {and}}$${{Dnew} = {{Pb} - \frac{TinjCORb}{Gnew}}},\quad {and}$

validating a value (Pk,n), measured when the engine (1) is in a steadystate, as a top value (Ph,n) or respectively as a bottom value (Pb,n)for the charging parameter, correlating to it a basic value respectivelyfor the top or bottom control variable in the order n (TinjBk,n) takenfrom an operating line filtered and stored in the computer during thepreceding cycle n−1 and defined by stored coefficients (DFil,n−1 andGFil,n−1), and then correlating it to a corrected value for the controlvariable (TinjCORk,n) in order to obtain a first point, and taking asthe second point respectively the point having the top or bottom valuefor the charging parameter from the two points stored in the computerduring the preceding cycle n−1, and having coordinates (Pb,n−1,TinjCORb,n−1; Ph,n−1, TinjCORh,n−1), and then adopting as the newfiltered operating line, defined by new filtered coefficients (DFil,nand GFil,n), an intermediate line between the stored line havingcoefficients (DFil,n−1 and GFil,n−1) and the new line defined by thenewly computed coefficients (Dnew and Gnew), and storing the newfiltered coefficients (GFil,n and DFil,n) and substituting them for thepreceding filtered coefficients (GFil,n−1 and DFil,n−1) to determine thenext operating line for the next automatic adaptation cycle.
 2. A methodof automatic adaptation as claimed in claim 1, characterized in thatwhen the engine is running at a stabilized speed, it also consists invalidating the measured value of the charging parameter (Pk,n) as thenew top (Ph,n) or bottom (Pb.n) value respectively only if (Pk,n) isrespectively above a suppressed adaptation band of a predetermined widthand having (Pb,n−1) as a lower limit, or respectively below saidsuppressed adaptation band and having (Ph,n−1) as an upper limit.
 3. Amethod of automatic adaptation as claimed in claim 2, characterized inthat, with each new cycle of automatic adaptation of order n, itconsists in making a new suppressed adaptation band contiguous with thevalue entered for the charging parameter (Pk,n) and comparing thislatter value with the lower limit (Pb,n−1) of the previous suppressedadaptation band so that if (Pk,n) is lower than (Pb,n−1), (Pk,n) willthen become the new lower limit (Pb,n) and the new upper limit willbecome: Ph,n=Pk,n+ΔP, ΔP being the width of the suppressed adaptationband, and if (Pk,n) is higher than (Pb,n−1), (Pk,n) will then become thenew upper limit (Ph,n) and the new lower limit becomes: Pb,n=Pk,n−ΔP. 4.A method of automatic adaptation as claimed in claim 2 characterized inthat it additionally consists in validating the measured value of thecharging parameter (Pk,n) as a new bottom value (Pb,n) only if, inaddition, (Pk,n) is below or equal to a value threshold of the chargingparameter.
 5. A method of automatic adaptation as claimed in claim 2characterized in that it consists in deeming the engine speed to havestabilized if, after a predetermined number of transitions in theair/fuel ratio coefficient (KO2) around its mean value have been foundand if the engine speed (N) and the position of a throttle membercontrolling the air supply rate to the engine are substantiallyconstant, the difference between the measured value of the chargingparameter (Pk,n) and a measured and filtered value of this parameter(PkFil,n) is below a value threshold, in whichPkFil,n=PkFil,n−1+k(Pk,n−PkFil,n−1), and where k is a factor between 0and
 1. 6. A method of automatic adaptation as claimed in claim 5,characterized in that a cycle of measuring and computing coefficientsfor the new filtered operating line (DFil,n and GFil,n) is initiated ifthe measured and filtered value (PKFil,n) of the charging parameter isoutside the suppressed adaptation band located in the preceding cyclen−1.
 7. A method of automatic adaptation as claimed in claim 2characterized in that it consists in defining the new filtered operatingline, having coefficients DFil,n and GFil,n, by applying a logicalfiltering process to the new computed coefficients Dnew and Gnew whichconsists in taking into account only a fraction of the differencebetween Dnew and Gnew respectively and the preceding filteredcoefficients DFil,n−1 and GFil,n−1 respectively using an approximationof the first order, on the basis of adaptation correction factors KD andKG, which range between 0 and 1 and may be equal, such that:DFil,n=DFil,n−1+KD(Dnew−DFil,n−1) and GFil,n=GFil,n−1+KG(Gnew−GFil,n−1).8. A method of automatic adaptation as claimed in claim 7, characterizedin that it consists in applying adaptation correction factors KD and KGat several levels, depending on the control rate of the engine (1)translated by the value of the air/fuel ratio coefficient (KO2).
 9. Amethod of automatic adaptation as claimed in claim 8 characterized inthat it consists in choosing the level of the factors KD and KGdepending on the value of KO2 as ascertained in each of the ranges ofthe top and bottom values of the charging parameter respectively aboveand below the corresponding suppressed adaptation band.
 10. A method ofautomatic adaptation as claimed in claim 9, characterized in that itconsists in choosing a strong, mean or weak value respectively for atleast one of the factors KD and KG depending on whether the air/fuelratio coefficient KO2 is measured outside a band of the air/fuel ratiocoefficient centred on the mean value of KO2 and of predetermined width,in the two charging parameter ranges which are above and below saidsuppressed adaptation band, or measured outside said air/fuel ratiocoefficient band in one of said charging parameter ranges above or belowsaid suppressed adaptation band but inside said air/fuel ratiocoefficient band in the other of said upper and lower charging parameterranges or, finally, measured inside said air/fuel ratio coefficient bandin the two upper and lower charging parameter ranges.
 11. A method ofautomatic adaptation as claimed in claim 7 characterized in that, everytime the engine (1) is started, it consists in determining, by means ofthe filtered operating line, having coefficients (DFil) and (Gfil),stored in memory on re-starting, two theoretical values for the controlvariable (TinjCORh) and (TinjCORb) corresponding to two values of thecharging parameter selected from outside the usual range of values forsaid charging parameter and which are a top initialisation value PhINITand a bottom initialization value PbINIT respectively, selecting asuppressed adaptation band essentially centred between PbINIT andPhINIT, with a lower limit (Psb) higher than PbINIT and an upper limit(Ph) lower than PhINIT, after which the measuring and computing cycle isthen run as in the continuous state, a new validated value beingacquired for the charging parameter if said new value falls outside thesuppressed adaptation band and the coefficients (DFil,n and GFil,n) forthe new filtered operating line being computed on the basis of the newmeasured and filtered value of the charging parameter (PkFil) and one ofthe two initialisation value points (PhINIT or PbINIT) of saidparameter.
 12. A method of automatic adaptation as claimed in claim 11characterized in that when the engine is re-started, it consists inprogressively adapting the computer (21) to the real conditions bysetting the initial values for the adaptation correction factors KD andKG as a function of a fictitious degree of adaptation of the engine. 13.A method of automatic adaptation as claimed in claim 11 characterized inthat, before the computer (21) is switched on for the first time, itconsists in pre-loading initial values (GINIT and DINIT) of theoperating line coefficients into the computer memory, which are definedexperimentally for the specific type of engine, and substituting themfor the coefficients (GFil and DFil) stored for start-up purposes andnot yet existing.
 14. A method of automatic adaptation as claimed inclaim 2, for an engine (1) co-operating with a purging circuit, fittedwith a canister (16) to collect fuel vapors from at least one tank (11)and connected to an intake pipe (4) of the engine (1) by an electricallycontrolled purging valve (20) of the canister (16), and whose rate isdriven by the computer (21) so that the timing of the purging valve (20)simultaneously with the automatic adaptation is inhibited, characterizedin that it also consists in widening the suppressed adaptation bandrespectively towards the top values or towards the bottom values of thecharging parameter if the engine regulation rate is satisfactory,depending on the value of air/fuel ratio coefficient (KO2), within therespective top or bottom range of the charging parameter which is aboveor below said suppressed adaptation band respectively before it iswidened.
 15. A method of automatic adaptation as claimed in claim 14,characterized in that it also consists in not widening the effectivesuppressed adaptation band except during a predetermined period of time,assisted by a counter which is re-started with each automatic adaptationcycle to count down said period of time.
 16. A method of automaticadaptation as claimed in claim 14 characterized in that it also consistsin defining an estimated coefficient (KCAN) of the fuel contents in thepurging circuit, computing this coefficient (KCAN) when purging ispermitted on the basis of the deviation in the air/fuel ratiocoefficient (KO2) so that KCAN is increased or decreased respectively ifKO2 is respectively below or above its mean value and in that it furtherconsists in entering an automatic adaptation phase if KCAN falls below apredetermined threshold relating to the fuel content.
 17. A method ofautomatic adaptation as claimed in claim 1 characterized in that it alsoconsists in converting the base value (TinjB) into a corrected value ofthe control variable (TinjCOR) by a multiplicative correction using theair/fuel ratio coefficient (KO2) such that: TinjCOR=TinjB×KO2.
 18. Adevice for automatically adapting the air/fuel ratio of an injectionengine (1), comprising: a computer (21) connected to sensors (26, 28)detecting operating parameters of the engine (1) as well as an oxygensensor (33) in the exhaust gas of the engine (1), said computer (21)computing values of a control variable intended to be applied to atleast one fuel injector (2) of the engine (1), and obtained from basevalues (TinjB) expressed as increasing linear functions of a chargingparameter, with a shift (D) from the original charging parameter and again (G) corresponding to the slope of the corresponding characteristicline, said base values of the control variable (TinjB) being correctedby means of a air/fuel ratio coefficient (KO2) determined by thecomputer (21) as a function of the air/fuel ratio signal (R) from theoxygen sensor (33) in closed loop operation and equal to a mean value inopen loop operation, in order to center operation of the engine (1) onan air/fuel ratio equal to 1, the computer (21) automatically adaptingthe shift (D) and the gain (G) in cycles to ensure that KO2 remainsclose to its mean value by correcting any deviation in KO2, and saidcomputer (21) comprising at least one microprocessor programmed forperforming calculations and manipulating values necessary forautomatically adapting the air/fuel ratio.